1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a belt for a continuously variable transmission which is wound across a primary pulley and a secondary pulley each composed of a pair of sheaves and, more specifically, to a belt for a continuously variable transmission whose noise is reduced by using V blocks having different thickness for the large number of V blocks that abut against the pulleys.
2. Description of Related Art
A belt type continuously variable transmission (hereinafter abbreviated as CVT) is generally used for power transmission systems of cars and the like. Belts for the CVTs typically include V blocks that are continuously attached to an endless body. In terms of the endless body, there is a push-type endless body that uses a ring composed of a plurality of laminated metal plates that transmits power by exerting a compression force on the V blocks, and a pull-type endless body that uses a chain in which link plates are linked alternately by pins and that transmits power by a tensile force acting on the chain. Although the present invention has been developed for the push-type endless body, it is also applicable to the pull-type endless body.
Belts for CVTs generate an abutment sound when the V blocks (elements) abut against the pulleys. The sound becomes irritating to human ears at a peak frequency when the thicknesses of the V blocks are the same.
Conventionally, belts have provided a lower noise by dispersing the peak frequency, described above, by randomly disposing a plurality of types of blocks having different thicknesses, as disclosed in Japanese Patent Publication No. 1994-21605 and Japanese Patent Laid-Open No. 2000-274492, for example. Although the belt in which the blocks, having different thickness, are attached at random (hereinafter referred to as a randomly mixed belt) can lower the frequency peak by dispersing the noise, its effect is not enough and a noise is still produced that irritates human ears.
As shown in FIG. 6, a belt 11 assembled by 400 blocks (elements) 3 having a thickness of only 1.5 mm generates noise having a very narrow peak on a bite-in order of the blocks to the pulley.
Although a randomly mixed belt 12, in which the same number (200) of blocks (elements) having a thickness of 1.4 mm and blocks (elements) having a thickness of 1.5 mm are mixed and arranged at random, can lower the frequency peak by white noise centering on an order equivalent to 1.45 mm, which is the mean value between 1.4 mm and 1.5 mm as shown in FIG. 7, noise is still generated that is irritating to human ears.